Place one cake on serving plate, spread pudding mixture on top, then top off with second cake.

For the glaze:

Microwave chocolate and butter on high for one minute in a small microwave safe bowl. Stir until chocolate is melted. Add powdered sugar and 4 tablespoons milk; mix well until smooth. Spread over the top of the cake immediately letting drip down the sides. Refrigerate at least one hour before serving.